You should only use one ORCID iD in any case. If you have found that you have two ORCID iDs, you can deactivate one ORCID iD so that the data are deleted and the record points to another ORCID iD. To do this, you need access to both ORCID iDs. If you find that you have another ORCID iD but no longer have the access data for it, you will need to contact ORCID. The details are explained in the linked ORCID Support article.